Chromatography is a method of separating substances that make up a liquid or gaseous mixture. One use of it is to measure or identify low concentrations of substances, such as pollutants in air or water. Another use is to separate and identify products of chemical reactions. Chemists use this method to separate pure substances from impurities.
Chromatographic methods are based mainly on a process called adsorption. A mixture passes through a solid or liquid material
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components can be determined from the relative areas under the peaks. By varying the polarity of the column and its temperature, many different resolutions can be carried out. Since the capacity of gas chromatograph columns is very low, the gas chromatograph is used chiefly as an analytical tool, although it can be used for preparative purposes as well. Miniaturized gas chromatograph instruments have been employed in space probes to analyze the atmospheres of other planets.